Medicine: Christmas Disease

Christmas disease is another name given to Haemophilia B (or hemophilia B), which is a blood clotting disorder. It is sometimes called Christmas disease after Stephen Christmas, the first patient described with this disease. In addition, the first report of its identification was published in the Christmas edition of the British Medical Journal.
As in haemophilia A, only males are usually affected by Christmas disease. This blood disease has also mainly affected both the Russian and British Royal Families on the basis of genetic factors.

Cool Link:
Haemophilia in European royalty